The 9mm was only produced as a 7-element type 1 before the type 6 was introduced. Type 2 Naglers have 8 elements.
At one point there was a redesign of the formerly smooth-style casing of the 9mm Nagler to add the rubber grip ring, rubber eyeguard, and even later threads and a safety undercut in the 2" skirt. In the meantime coatings may have been updated, but the optical design always remained a 7-element type 1. -- Mike